CN109747650B - Method and system for controlling vehicle tire-road friction estimation - Google Patents
Method and system for controlling vehicle tire-road friction estimation Download PDFInfo
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- CN109747650B CN109747650B CN201811294478.4A CN201811294478A CN109747650B CN 109747650 B CN109747650 B CN 109747650B CN 201811294478 A CN201811294478 A CN 201811294478A CN 109747650 B CN109747650 B CN 109747650B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
- B60W40/10—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to vehicle motion
- B60W40/105—Speed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
- B60W40/02—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to ambient conditions
- B60W40/06—Road conditions
- B60W40/068—Road friction coefficient
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K31/00—Vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed, i.e. preventing speed from exceeding an arbitrarily established velocity or maintaining speed at a particular velocity, as selected by the vehicle operator
- B60K31/0066—Vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed, i.e. preventing speed from exceeding an arbitrarily established velocity or maintaining speed at a particular velocity, as selected by the vehicle operator responsive to vehicle path curvature
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K31/00—Vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed, i.e. preventing speed from exceeding an arbitrarily established velocity or maintaining speed at a particular velocity, as selected by the vehicle operator
- B60K31/18—Vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed, i.e. preventing speed from exceeding an arbitrarily established velocity or maintaining speed at a particular velocity, as selected by the vehicle operator including a device to audibly, visibly, or otherwise signal the existence of unusual or unintended speed to the driver of the vehicle
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
- B60W30/14—Adaptive cruise control
- B60W30/143—Speed control
- B60W30/146—Speed limiting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
- B60W40/02—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to ambient conditions
- B60W40/06—Road conditions
- B60W40/072—Curvature of the road
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W10/00—Conjoint control of vehicle sub-units of different type or different function
- B60W10/18—Conjoint control of vehicle sub-units of different type or different function including control of braking systems
- B60W10/184—Conjoint control of vehicle sub-units of different type or different function including control of braking systems with wheel brakes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2552/00—Input parameters relating to infrastructure
- B60W2552/20—Road profile
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2552/00—Input parameters relating to infrastructure
- B60W2552/30—Road curve radius
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2552/00—Input parameters relating to infrastructure
- B60W2552/40—Coefficient of friction
Abstract
A method for controlling a vehicle (200) traveling on a roadway (202) is provided. The method comprises the following steps: identifying (100) an upcoming curve (204) and determining (102) characteristics of the curve; determining (104) a current vehicle speed vv(ii) a Estimating (106) the friction μ between the tyre of the vehicle and the roade(ii) a Estimating (108) a maximum allowable vehicle speed v when entering a curve based on curve characteristics, vehicle speed and estimated frictionmax_e(ii) a Determining (112) that a friction measurement is required if the current vehicle speed is above the estimated maximum allowable vehicle speed; if the distance d between the vehicle and the entrance of the curvevDistance d above a predetermined thresholdTAnd if a braking action is detected, performing (116) a friction measurement during the braking action to determine a current friction μc(ii) a Performing (118) a friction measurement to determine a current friction if the distance between the vehicle and the curve entrance is below a predetermined threshold distance; and determining (120) a maximum allowable vehicle speed v based on the curve radius, the vehicle speed and the current frictionmax_d。
Description
Technical Field
The invention relates to a method and a system for controlling a vehicle. In particular, the present invention relates to a method and system for determining tire-road friction prior to an upcoming curve.
Background
Both autonomous vehicles and human drivers need to adjust the speed before entering a curve in order to be able to stay on the road. The maximum speed at which a curve can be entered is mainly determined by the tire-road friction that the car will experience and the radius of the path.
For autonomous vehicles, knowledge of friction is considered to be particularly important to ensure that a road is not left. A large friction uncertainty means that the vehicle speed must be lower and may be too low for driver acceptance. The radius on the path can be estimated using, for example, an on-board camera or map information, wherein curve tangent behavior can also be taken into account. It is well known that obtaining a reliable estimate of tire-road friction can be more difficult. The simplest method is to brake completely and measure the deceleration, but this can be disturbing to the driver and the surrounding road users.
To overcome this problem, several attempts have been made to accomplish non-intrusive (nonauthrive) measurements of tire-road friction using, for example, forward looking cameras, LIDAR and accelerometers within the wheels.
Recently, a promising new technique for reliably measuring tire-road friction without reducing vehicle speed has been developed, see EP3106360a 1. This technique measures friction by simultaneously braking on the rear axle and accelerating on the front axle. With this technique, measurement of tire-road friction can be completed without reducing the vehicle speed. However, the driver and passengers may notice the measurement by the sound of the brake/propulsion system. When performing the measurement, the vehicle may also appear to be "sitting" on its rear axle, since temporarily braking on the rear axle and acceleration on the front axle will cause the vehicle to extend slightly. Furthermore, if the measurements are performed frequently, they will have a negative impact on fuel consumption. Therefore, there is a need to minimize the number of measurements while still providing a measure of tire-road friction with sufficient confidence to assist drivers and autonomous vehicles in adjusting speed to be able to stay on the road.
Disclosure of Invention
In view of the above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide a method for controlling a vehicle to perform friction measurements only when needed.
According to a first aspect of the invention, this object is achieved by a method for controlling a vehicle travelling on a road. The method comprises the following steps: identifying an upcoming curve and determining characteristics of the curve; determining the current vehicle speed; estimating friction between a tire of the vehicle and the road; estimating a maximum allowable vehicle speed when entering a curve based on the curve characteristic, the vehicle speed, and the estimated friction; determining that a friction measurement is required if the current vehicle speed is above the estimated maximum allowable vehicle speed, wherein the friction measurement requires braking of the vehicle; performing a friction measurement during a braking action to determine a current friction if a distance between the vehicle and a curve entrance is above a predetermined threshold distance and if the braking action is detected; performing a friction measurement to determine a current friction if a distance between the vehicle and the curve entrance is below a predetermined threshold distance; and determining a maximum allowable vehicle speed based on the curve radius, the vehicle speed, and the current friction.
In the present method, the friction measurement technique described in EP3106360a1 may be used to determine tire-road friction. This technique measures friction by simultaneously braking on the rear axle and accelerating on the front axle. Thus, the friction measurement does not involve braking of the vehicle, i.e. it does not involve reducing the speed of the vehicle. However, during normal driving, the driver may still notice that the friction measurement was performed. Thus, by performing the friction measurement during braking, if possible, the friction measurement can be performed in a non-intrusive manner without the driver noticing it. It should be noted, however, that other types of friction measurement techniques may also be used.
The invention is therefore based on the recognition that: the friction measurement is not always required to be performed when approaching a curve, and in many cases, if the friction measurement is required, the friction measurement may be performed during normal running of the vehicle. For example, many drivers will slow down before a curve sufficiently that friction measurements can be performed during driver initiated braking. Unless friction measurements are performed during driver-initiated braking, non-braking friction measurements are advantageously employed to minimize the impact on the vehicle experienced by the driver. Therefore, it is possible to avoid unnecessary friction measurement, minimize the number of friction measurements performed, and minimize driver inconvenience of forced friction measurement.
Thereby, it can be ensured that the maximum allowable vehicle speed when reaching the entrance of a curve is determined using the friction value as correct as possible to prevent the vehicle from losing grip in the curve. It is assumed here that the tire-road friction in a curve is not significantly different from the tire-road friction before the curve. In other words, the described method is not intended to take into account unexpected and transient events that affect the frictional characteristics of a curve, such as oil spills or ice patches. It is also assumed that the speed of the vehicle (i.e., the maximum allowable vehicle speed) at the time of entering the curve can be safely maintained throughout the curve. Furthermore, even if the vehicle loses grip in a curve, it is assumed that other vehicle systems assume control, such as an Electronic Stability Control (ESC) system.
According to an embodiment of the invention, the method may further comprise: if the current vehicle speed is higher than the determined maximum allowable vehicle speed, the vehicle is braked so that the vehicle speed when the curve is reached is lower than or equal to the determined maximum allowable vehicle speed. Thus, automatic braking of the vehicle may be performed without driver interaction to ensure that the vehicle speed is not too high when the curve entrance is reached. Thus, the described method may advantageously be implemented as a safety feature in an autonomous or semi-autonomous vehicle.
According to an embodiment of the invention, the method may further comprise: if the current vehicle speed is above the maximum allowable vehicle speed, braking the vehicle from the current position of the vehicle to the curve entrance at a constant deceleration such that the vehicle speed is equal to or below the determined maximum allowable vehicle speed when the vehicle reaches the curve entrance. By braking at a constant deceleration, a smooth and comfortable braking experience is achieved.
According to an embodiment of the invention, the method may further comprise: if the current vehicle speed is above the determined maximum allowable vehicle speed, the driver is warned indicating that there is a risk of leaving the road unless the vehicle speed is reduced to the determined maximum allowable vehicle speed. Thus, the method is also advantageously used in vehicles without self-driving functionality to warn the driver when the vehicle speed is above the determined maximum allowable speed. The alert may be in the form of a visual or audible indication, or a combination thereof. The warning is preferably provided at a good time before braking is required so that the driver has time to safely reduce the vehicle speed when required. It can be assumed that the driver needs more time (i.e., longer distance) to safely reduce the vehicle speed than an automated system. Thus, the predetermined threshold distance to the entrance of the curve may be set higher when the method is implemented in a vehicle in which the driver intends to control the vehicle speed.
According to one embodiment of the invention, the predetermined threshold distance is based on a distance required to reduce the vehicle speed from a current speed to an estimated maximum allowable vehicle speed when entering a curve. Thus, the threshold distance may be based on vehicle speed, estimated friction, and vehicle braking capability. The threshold distance may also be set such that the vehicle may be braked in a manner that is comfortable for the vehicle occupants, since it may not be desirable to apply as high a braking force as possible. For the above reasons, the threshold distance in an autonomous vehicle may also be set differently than in a vehicle operated by the driver.
According to one embodiment of the invention, estimating the friction between the tires of the vehicle and the road may comprise acquiring a previously measured friction value of a curve, and estimating that the friction is lower than the previously measured friction. The previously measured friction value may for example be available in the vehicle if the vehicle has previously traveled through a curve under similar road conditions. Previously measured friction values may also be obtained from a remote location such as a cloud server, which may store measured friction values from different vehicles and under various road conditions. The friction estimate may also take into account current local weather information, such as temperature information and windshield wiper activity.
According to one embodiment of the invention, estimating the friction between the tires of the vehicle and the road may comprise obtaining a most recently measured friction value of the road on which the vehicle is running, and estimating the friction to be lower than the most recently measured friction value. In a similar manner to that described above, the most recently measured friction value may be the friction measured by the vehicle or a value obtained from a remote location. The most recently measured friction value may also be received from another vehicle traveling on the road by utilizing a vehicle-to-vehicle (V2V) communication system. Thus, the term "estimate" should be interpreted broadly herein, wherein the estimated friction is represented by a friction value assumed to represent tire-road friction in a curve.
According to one embodiment of the invention, the estimated friction is preferably at least two standard deviations (standard deviations) lower than the expected friction. It can thus be determined that the estimated friction value is lower than the expected average value with 95% certainty. The expected value may be based on any of the previously discussed measured friction values. Of course even lower estimated friction values may be used and the difference between the estimated friction value and the expected value may be based at least in part on external factors such as road and weather conditions.
According to one embodiment of the invention, determining a characteristic of a curve may include determining a curve radius. Further, determining characteristics of the curve may include determining a curve shape, a road width, a lane width, and a road camber (camber). It is generally desirable to have as much information describing a curve as possible in order to be able to accurately estimate the maximum allowable vehicle speed through the curve based on the current friction. The curve characteristics may be stored in the vehicle or retrieved from a remote server (e.g., using a cloud communication infrastructure). It is also possible to determine the curve characteristic using only in-vehicle sensors such as cameras, radar/LIDAR and the like. For example, the curve radius may be estimated using only information acquired by the onboard camera. Thus, the characteristic of the curve may include any parameter describing the curve that can be used to estimate the maximum allowable vehicle speed when entering the curve.
According to one embodiment of the invention, the method may further comprise estimating a vehicle path through the curve based on the curve characteristic. The vehicle speed can thus be adapted to an estimated and preferably optimized path through the curve, wherein the path can be improved depending on how much information describing the characteristics of the curve is available. The path through the curve may, for example, include intersecting the curve so that the vehicle is not always in the middle of the lane. This may allow the vehicle to travel through a curve in a manner more similar to how the driver would travel through the curve, thereby providing a more familiar user experience.
According to one embodiment of the invention, determining characteristics of a curve may include obtaining information from a previously established map (e.g., a map in a navigation system of a vehicle).
According to a second aspect of the invention, the object is achieved by a vehicle control system comprising a vehicle control unit configured to: identifying an upcoming curve and determining characteristics of the curve; determining the current vehicle speed; estimating friction between a tire of the vehicle and the road; estimating a maximum allowable vehicle speed when entering a curve based on the curve characteristic, the vehicle speed, and the estimated friction; determining that a friction measurement is required if the current vehicle speed is higher than the estimated maximum allowable vehicle speed; performing a friction measurement during a braking action to determine a current friction if a distance between the vehicle and a curve entrance is above a predetermined threshold distance and if the braking action is detected; performing a friction measurement to determine a current friction if a distance between the vehicle and the curve entrance is below a predetermined threshold distance; and determining a maximum allowable vehicle speed based on the curve radius, the vehicle speed, and the current friction.
Additional effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect of the invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention can be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.
Drawings
These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:
FIG. 1 is a flow chart summarizing the general steps of a method according to one embodiment of the invention;
FIG. 2 schematically illustrates a method performed by a vehicle in accordance with one embodiment of the invention; and
fig. 3 schematically shows a control system according to an embodiment of the invention.
Detailed Description
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for the sake of completeness and to fully convey the scope of the invention to the skilled person. Like reference numerals refer to like elements throughout.
FIG. 1 is a flowchart outlining the general steps of a method of controlling a vehicle 200 according to one embodiment of the present invention; and the method will be further described with reference to fig. 2, fig. 2 schematically illustrating the method performed by a vehicle 200.
The method is applied when the vehicle is driving on a road 202 and approaching a curve 204 in the road 202. In particular, the method aims at determining whether and where friction measurements have to be performed, thereby determining a maximum allowable vehicle speed to enable the vehicle to drive through the curve 204 without losing grip.
The following reference numerals will be used for the description of the method:
-vvcurrent vehicle speed
-μeEstimated tire-road friction
-vmax_eEstimated maximum allowable vehicle speed
-dvDistance from vehicle to curve entrance
-dTDistance to threshold
-μcCurrent (measured) tire-road friction
-vmax_dDetermined maximum allowable vehicle speed
-R-bend radius
-g ═ gravitational constant
-dmin_eEstimated minimum braking distance
-amax_eMaximum deceleration estimated
The first step of the method involves identifying 100 an upcoming curve 204 and determining 102 the characteristics of the curve. The curve information can be obtained, for example, from a navigation system in the vehicle or from a remote server as described earlier. A straightforward way to determine the characteristics of a curve may be to approximate the curve as if the entire curve had a fixed radius R. However, the curve characteristic preferably includes additional information describing the curve shape, road width, lane width, and road camber. Furthermore, the method may for example be further refined to take into account that most roads and vehicle trajectories are shaped as clothoids rather than straight lines and circles. For simplicity, however, this specification uses a simple description of the road shape to describe the core idea of the invention.
Once a curve is identified and the curve characteristic is determined, a current vehicle speed v is determined 104vAnd estimating the friction value mu of 106 curvese. The friction value is intentionally underestimated relative to the expected friction so that the probability of the actual friction being lower than the estimated friction is very low.
Radius of curve R and vehicle speed vvAnd estimated friction mueEstimated maximum allowable vehicle speed v, when knownmax_eCan be estimated 108 as
Due to estimated friction μeAssuming a current vehicle speed vvAbove estimated maximum allowable vehicle speed vmax_eEstimated maximum allowable deceleration a for a vehicle ahead of a curvemax_eThere are also limitations. The estimated maximum allowable deceleration amax_eCan be determined as
amax_e＝-μeg.
Maximum allowable deceleration amax_eAnd the minimum distance d from the curve is determinedmin_eAt which the braking must be initiated to reach the maximum allowable vehicle speed v before reaching the curve entrance 206max_eWherein the minimum distance d from the curvemin_eIs determined as
Therefore, if the vehicle speed v isvAbove maximum allowable vehicle speed vmax_eThe braking of the vehicle must then correspond to the estimated minimum distance d at the latest at the distance from the entrance of the curvemin_eAnd begins.
Thus, if the current vehicle speed v isvAbove estimated maximum allowable vehicle speed vmax_eThen it is determined 112 that a friction measurement is required. How this can be explained is described in detail in EP3106360A1The details of performing the friction measurement by simultaneously braking on the rear axle and accelerating on the front axle will not be discussed in detail in this disclosure. It should be noted, however, that the described method involves measuring friction without changing the vehicle speed. Thus, braking of the rear axle (which is counteracted by acceleration of the front axle) does not result in a change in vehicle speed. The cited method may be referred to as a non-braking friction measurement method. This is in contrast to previously known methods involving vehicle braking. In addition to the above referenced methods, other non-braking friction measurement methods may be used, such as optical measurements of road characteristics.
Next, if the distance d between the vehicle 200 and the entrance of the curvevDistance d above a predetermined thresholdTAnd if a braking action is detected, performing 116 a friction measurement during the braking action to determine a current friction muc. Predetermined threshold distance dTIs set to a minimum distance d above the estimatemin_eSo that there is sufficient time to perform the friction measurement. The threshold distance exceeding the minimum distance dmin_eMay be based on the current vehicle speed v, for examplevEstimated friction mueAnd the estimated time/distance required to perform the friction measurement. A sufficiently long vehicle braking action for performing the brake friction measurement may be, for example, in the range of 1-2 seconds.
Thus, if the vehicle 200 is at a safe distance from the curve entrance 206 and if the driver brakes the vehicle, friction measurements are performed during driver initiated braking. Thus, the current friction is known and no additional friction measurement is required. If no braking action is detected, the distance from the vehicle 200 to the curve 204 will eventually be less than the threshold distance dT。
Next, if the current distance d between the vehicle 200 and the curve entrance 206vDistance d below a predetermined thresholdTAnd no friction measurement is performed due to the identification of the curve 204, then a friction measurement is performed 118 to determine the current tire-road friction μc. At least, a threshold distance dTIs the estimated minimum braking distance dmin_ePlus performing friction measurementsThe required distance.
Based on the determined (i.e. measured) current tire-road friction μcMaximum allowable vehicle speed vmax_dCan be determined 120 as a function of curve radius, vehicle speed, and current friction
Thereby, the maximum allowable vehicle speed v is executedmax_dAnd if the current vehicle speed is higher than the determined maximum allowable vehicle speed vmax_dBraking the vehicle such that the vehicle speed when a curve is reached is lower than or equal to the determined maximum allowable vehicle speed vmax_d. The vehicle 200 may be braked automatically or by driver initiated braking. In non-automated systems, a safety margin is advantageously added so that the driver has time to react and to perform the required braking in a safe manner. In other words, the threshold distance dTPreferably higher in non-automated systems.
The vehicle control system 300 comprises a control unit 208, which control unit 208 is configured to control the vehicle to perform the described steps of the method. The control unit 208 may include a microprocessor, microcontroller, programmable digital signal processor, or other programmable device. The control unit 208 may also or alternatively comprise an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device or a digital signal processor. Where the control unit 208 comprises a programmable device such as the microprocessor, microcontroller, or programmable digital signal processor described above, the processor may further comprise computer executable code that controls the operation of the programmable device.
Further, the control unit 208 may be embodied as one or more control units, wherein each control unit may be a general purpose control unit or a dedicated control unit for performing a specific function.
Fig. 3 schematically shows a control system 300, wherein the control unit is connected to various subsystems responsible for performing the various functions of the method.
As shown in fig. 3, the control system 300 includes: an environment sensor unit 302 that uses, for example, GPS, a camera, radar, or the like to determine the vehicle position; an motion planner 304 that performs strategic and strategic motion planning, such as determining an acceleration/deceleration curve. The control system 300 further comprises: a vehicle state estimator 306 that determines a motion state of the vehicle, for example, a vehicle speed on the ground and a tire-road friction; a friction measurement monitor 308 that determines when to begin a friction measurement; a vehicle motion controller 310 that receives motion requests and outputs requests to actuators (e.g., powertrain and brakes) to execute the motion requests; and finally a friction measurement actuator 312 that determines an action (e.g., wheel torque) to perform a friction measurement.
The present description is based on a simplified model of a curve, it being noted that the described method and system may also be modified to control the vehicle to have a vehicle speed when entering a curve, and to modify the vehicle speed when in a curve. This may be desirable, for example, for curves having complex shapes deviating from a simple arc, for long curves, or for a number of consecutive curves.
The described method therefore aims to maximise the likelihood that the vehicle will be able to be on the road under the following assumptions: given the current speed of the vehicle, the shape of the road ahead, and a priori knowledge of the minimum available tire-road friction, the friction in a curve is not significantly lower than the friction before the curve.
While the present invention has been described with reference to specific exemplary embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Moreover, it should be noted that portions of the present method and system may be omitted, interchanged or arranged in various ways that still perform the functions of the present invention.
In addition, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
Claims (14)
1. A method for controlling a vehicle (200) to travel on a roadway (202), the method comprising:
identifying (100) an upcoming curve (204) and determining (102) a curve characteristic;
determining (104) a current vehicle speed vv；
Estimating (106) the friction μ between the tyre of the vehicle and the roade；
Estimating (108) a maximum allowable vehicle speed v when entering the curve based on the curve characteristic, the vehicle speed and the estimated frictionmax_e；
Determining (112) that a friction measurement is required if the current vehicle speed is above the estimated maximum allowable vehicle speed;
if the distance d between the vehicle and the entrance of the curvevDistance d above a predetermined thresholdTAnd if a braking action is detected, performing (116) a friction measurement during the braking action to determine a current friction μc；
Performing (118) a friction measurement to determine a current friction if the distance between the vehicle and the curve entrance is below the predetermined threshold distance; and
determining (120) a maximum allowable vehicle speed v based on a curve radius, vehicle speed and current frictionmax_d。
2. The method of claim 1, further comprising braking the vehicle such that the vehicle speed is less than or equal to the determined maximum allowable vehicle speed when the curve is reached if the current vehicle speed is greater than the determined maximum allowable vehicle speed.
3. The method according to claim 1 or 2, further comprising braking the vehicle at a constant deceleration from the current position of the vehicle to the curve entrance if the current vehicle speed is higher than the maximum allowable vehicle speed, such that the vehicle speed is equal to or lower than the determined maximum allowable vehicle speed when the vehicle reaches the curve entrance.
4. The method of claim 1, further comprising warning the driver if the current vehicle speed is above the determined maximum allowable vehicle speed, indicating that there is a risk of leaving the road unless the vehicle speed is reduced to the determined maximum allowable vehicle speed.
5. A method according to claim 1 or 2, wherein the predetermined threshold distance is based on the distance required to reduce the vehicle speed from the current speed to the estimated maximum allowable vehicle speed when entering a curve.
6. The method according to claim 1 or 2, wherein estimating the friction between the tyres of the vehicle and the road comprises acquiring a previously measured friction value of the curve, and estimating the friction to be lower than the previously measured friction value.
7. The method of claim 1 or 2, wherein estimating friction between a tyre of a vehicle and a road comprises obtaining a most recently measured friction value of a road on which the vehicle is driving, and estimating the friction to be lower than the most recently measured friction value.
8. The method of claim 1 or 2, wherein determining the characteristic of the curve comprises determining a curve radius.
9. The method of claim 1 or 2, wherein determining the characteristic of the curve comprises determining a curve shape.
10. The method of claim 1 or 2, wherein determining the characteristic of the curve comprises determining at least one of a road width, a lane width, and a road camber.
11. The method of claim 1 or 2, wherein determining the characteristic of the curve comprises obtaining a curve characteristic from a remote server.
12. The method according to claim 1 or 2, further comprising estimating a vehicle path through the curve based on the curve characteristic.
13. The method of claim 1 or 2, wherein determining characteristics of the curve includes obtaining information from a previously established map.
14. A vehicle control system (300) comprising a vehicle control unit (208), the vehicle control unit (208) being configured to:
identifying an upcoming curve (204) and determining (102) a characteristic of the curve;
determining a current vehicle speed vv；
Estimating the friction mu between the tires of a vehicle and the roade；
Estimating a maximum allowable vehicle speed v when entering the curve based on a curve characteristic, a vehicle speed, and an estimated frictionmax_e；
Determining that a friction measurement is required if the current vehicle speed is higher than the estimated maximum allowable vehicle speed;
if the distance d between the vehicle and the entrance of the curvevDistance d above a predetermined thresholdTAnd if a braking action is detected, performing (116) a friction measurement during the braking action to determine a current friction μc；
Performing (118) a friction measurement to determine a current friction if the distance between the vehicle and the curve entrance is below the predetermined threshold distance; and
determining (120) a maximum allowable vehicle speed v based on a curve radius, vehicle speed and current frictionmax_d。
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP17199502.0A EP3480074B1 (en) | 2017-11-01 | 2017-11-01 | Method and system for controlling a vehicle tire-to-road friction estimation |
| EP17199502.0 | 2017-11-01 |
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| Publication Number | Publication Date |
|---|---|
| CN109747650A CN109747650A (en) | 2019-05-14 |
| CN109747650B true CN109747650B (en) | 2022-04-12 |
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| CN201811294478.4A Active CN109747650B (en) | 2017-11-01 | 2018-11-01 | Method and system for controlling vehicle tire-road friction estimation |
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| Country | Link |
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| US (1) | US10967874B2 (en) |
| EP (1) | EP3480074B1 (en) |
| CN (1) | CN109747650B (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US11465630B2 (en) * | 2018-09-14 | 2022-10-11 | Uatc, Llc | Driving surface friction estimations using vehicle steering |
| US11427223B2 (en) * | 2018-09-14 | 2022-08-30 | Uatc, Llc | Driving surface friction estimations for autonomous vehicles |
| CN109471437B (en) * | 2018-11-20 | 2020-10-16 | 百度在线网络技术（北京）有限公司 | Method, device and control system for controlling mobile robot |
| US11597364B2 (en) * | 2019-03-11 | 2023-03-07 | Mitsubishi Electric Research Laboratories, Inc. | System and method for determining friction curve of tire |
| US11543343B2 (en) | 2019-09-05 | 2023-01-03 | Volvo Car Corporation | Road friction estimation |
| US11318947B2 (en) | 2019-12-23 | 2022-05-03 | Volvo Car Corporation | Estimating surface friction coefficients using rear-wheel steering excitations |
| CA3126958C (en) * | 2020-03-17 | 2022-08-23 | Freeport-Mcmoran Inc. | Methods and systems for determining and controlling vehicle speed |
| KR20210154296A (en) * | 2020-06-11 | 2021-12-21 | 주식회사 만도모빌리티솔루션즈 | driver assistance apparatus |
| TWI790825B (en) | 2021-11-19 | 2023-01-21 | 財團法人工業技術研究院 | Safe following distance estimation stystem and estimation method thereof |
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Also Published As
| Publication number | Publication date |
|---|---|
| EP3480074A1 (en) | 2019-05-08 |
| US20190126933A1 (en) | 2019-05-02 |
| CN109747650A (en) | 2019-05-14 |
| US10967874B2 (en) | 2021-04-06 |
| EP3480074B1 (en) | 2021-10-06 |
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